[Prenatal diagnosis and evolution of patent urachus].

Prenatal ultrasonographic features of patent urachus consist in anechoic proximal cord cyst communicating with the bladder associated with large umbilicus. Distinction should be made with omphalocele and bladder extrophy. Spontaneous evolution leads to rupture during mid-trimester and bladder protrusion. Karyotyping is not mandatory in isolated typical cases. Early postnatal surgery is usually required.